Wood working27.09.2016

KKN stamp indicates the manufacturer

KKN stamp says Finnish sawn timber is manufactured at Koskisen.

The shipping mark on the end of Finnish sawn timber says who the manufacturer is. Koskisen’s sawn timber is stamped with the letters KKN at the trimming, grading and packaging plant, where the dried timber is sorted according to both grade and strength, and then packed. Sawn timber stamps indicate the grade and manufacturer, and that the sawn timber fulfils the requirements of EU directives.

The stickered board stacks coming from the drying plant are unloaded onto the line at the beginning of the trimming, grading and packaging plant, and an automatic moisture sensor keeps track of the moisture level in the sawn timber and prevents wet pieces from being packaged.

“The plant’s moisture sensor gives us immediate feedback on the moisture level of the sawn timber, and helps to ensure high-quality drying,” explains processing supervisor Esa Hiltunen.

Butt-end trimming involves cutting off, for example, a cracked butt end. Laser technology is used to help see the cutting point.

Butt-end trimming involves cutting off, for example, a cracked butt end. Laser technology is used to help see the cutting point.

At the beginning of the line, the operator monitors the accuracy of the sorting and the functioning of the line. At that point in the line, if the end of the timber is of poor quality it can be cut off, meaning the butt end is trimmed to a rough standard.

Quality grading based on appearance

Sawn timber is graded using cameras. Every side of a piece of sawn timber is inspected by three cameras; a total of 12 cameras calculate the dimensions, identify knots, cracks, resin pockets, wane and other wood characteristics. 

Esa Hiltunen and Mika Lehtonen inspect the operation of the FinScan grading camera.

Esa Hiltunen and Mika Lehtonen inspect the operation of the FinScan grading camera.

“Sorting has become a lot easier since the days when it was done with by eye,” says Production Manager Jaakko Huttunen.

“Whereas humans may make errors depending on the time of day or their general attentiveness, camera sorting always results in the same quality – it is 99% accurate. That means the customer can be confident that they are getting a product of consistent quality.” 

The ends of the sawn timber are trimmed to the desired length according to the data provided by the camera. 

“We can also make special lengths according to the customer’s specifications; for example, the Japanese lengths of 3,650 and 3,985 mm, which deviate from the traditional module dimensions,” says Huttunen.

Koskisen's sawn timber is CE marked.

Strength grading using vibration

At Koskisen, all sawn timber pieces are mechanically strength-graded by measuring the density (weight) of the piece and the natural frequency at which it vibrates. The side of every strength-graded piece is stamped with the CE mark, which indicates the strength grade, manufacturer, the authority that oversees the sorting, and naturally the grade, length and moisture class. All of the necessary information is right there on the piece of timber.

“The most common strength grade used in construction in Finland is C24. The stronger grades of C35 and C40 are used for the manufacture of, for example, roof trusses and glue-laminated timber,” explains Huttunen.

Sawn timber is strength-graded using machines.

Sawn timber is strength-graded using machines.

At the trimming, grading and packaging plant, Nelli Elf monitors the accuracy of the timber grades and ensures that the packages receive the correct quality stamps.

At the trimming, grading and packaging plant, Nelli Elf monitors the accuracy of the timber grades and ensures that the packages receive the correct quality stamps.

Sorted into compartments by grade and length

In a 24-hour period, 1,500 m3 of sawn timber, i.e. 30 truckloads, pass through Koskisen’s trimming and grading plant. The timber pieces are a blur on the line, with 125 whizzing through in one minute.

After measuring, sorting and stamping, the individual pieces will end up in one of the plant’s 45 different compartments. From there, the compartments are emptied one by one onto the packaging line, where each piece of sawn timber is stamped with the familiar red KKN stamp, which indicates the manufacturer and the grade, before the package is sent on its way.

The trimming, grading and packaging plant in a nutshell

  • Shifts: 3/5, every weekday, morning, evening and night shifts
  • Production: 1,500 m3/day, 30 truckloads
  • Employees: 5 workers/shift
  • Max. speed: 125 pcs/min